The current phase of this project involves continuing studies on the effects of selective brain lesions on production of the isolation call. Since lesions in the thalamus and midbrain that disrupt production of this vocalization also may encompass fibers arising from more rostral structures, it is important to determine the effects on the isolation call of damage to these rostral structures, particularly the anterior limbic cortex. Ablation of the major extent of the anterior limbic cortex in one subject resulted in failure to produce spontaneous isolation calls over 20 postoperative weeks. A second monkey with a less extensive lesion regained the ability to vocalize after the first postoperative week. The study of the role of opiates and opiate antagonists on Isolation Peep production showed in four subjects a naloxone-reversible reduction or elimination of isolation calls following morphine injections, suggesting that an opiate-dependent mechanism underlies production of this vocalization.